Seat shaft for bicycles



FIG. 1 is a perspective view of seat shaft for bicycles showing my new design;

FIG. 2 is a rear elevation view thereof;

FIG. 3 is a side elevation view thereof;

FIG. 4 is a front elevation view thereof;

FIG. 5 is a side elevation view thereof opposite to that shown in FIG. 3;

FIG. 6 is a bottom plan view thereof; and

FIG. 7 is a top plan view thereof. 

The ornamental design for a seat shaft for bicycles, as shown. 